Sony's OWN SITE says the Sensor output is 14-bit. The sensor is an Exmor. Exmor uses CP-ADC ON-DIE. The last output of the sensor is FROM the ADC.
Therefor...the A7s IS 14-BIT!
Yup. As you say, Sony show they've got a 14bit sensor output delivering 15.3 stops of DR. Interesting.
I can see you and neuro and a whole host of other web folks getting ready to point out how it is impossible and when DxO measure it and say they've got 15.3 stops of DR, DxO will be telling lies and faking it and then someone will go out and do real world tests that also corroborates with it and you'll all still be saying that it is a lie.
I want to see what they've got to show before I denounce them. After all, they're already getting more than 14 stops of DR (DxO says 14.8?) with the Nikon D800 so why should another .5 stop of DR be unreasonable? Would be interesting to see what a real world test of the DR of those cameras turned out, kind of aligned with what the Zacutto(?) folks did with various cameras for video.
Obviously it isn't a linear conversion (even now) but I'm kind of curious to know what's going on.
A curve of some kind is pretty obvious, whether it is a gamma curve or something else ...
Well, it's no surprise that you buy into DXO's bull. There are two values on DXO's site for DR. One is a measure, as in something actually MEASURED from a REAL RAW file. The other is an EXTRAPOLATION. It isn't even a real extrapolation, it is just a number spit out by a simple mathematical formula...they don't actually even do what they say they are doing.
The first of these is Screen DR. Screen DR is the ONLY actual "measure" of dynamic range that DXO does. It is the SINGLE and SOLE value for DR that is actually based on the actual RAW data. In the case of the D800....do you know what Screen DR is? (My guess is not.)
The other of these is Print DR. Print DR is supposedly the dynamic range "taken" from a downsampled image. The image size is an 8x12 "print", or do DXO's charts say. As it actually happens to be, and this is even according to DXO themselves...Print DR is not a measure at all. It isn't a measurement taken from an actually downsampled image. You know what it is? It is an extremely simple MATHEMATICAL EXTRAPOLATION based on...what? Oh, yup...the only actual TRUE MEASURE of dynamic range that DXO has: Screen DR. Print DR is simply the formula DR+ log2 SQRT(N/N0)
. DR is ScreenDR. N is the actual image size, N0 is the supposed downsampled size. The formula is rigged to guarantee that "Print DR" is higher than Screen DR...not even equal to, always higher. And, as it so happens, potentially 100% unrelated to reality, since it is not actually measured.
DXO doesn't even have the GUTS to ACTUALLY downsample real images and actually measure the dynamic range from those downsampled images. They just run a mathematical forumla against Screen DR and ASSUME that the dynamic range of an image, IF they had downsampled it, wouold be the same as what that mathematical value says it should be.
Print DR is about as bogus as "camera measurement 'science'" can possibly get. It's a joke. It's a lie. It's bullshit. The D800 does not have 14.4 stops of DR, as DXO's Print DR would indicate. The Screen DR measure of the D800? Oh, yeah...it's LESS than 14 stops, as one would expect with a 14-bit output. It's 13.2 stops, over ONE FULL STOP less than Print DR. The D600? Says Print DR 14.2, but Screen DR is 13.4. D610? Print DR 14.36, but Screen DR 13.55. D5300? Print DR 13.8, but Screen DR 13. A7? Print DR 14, but Screen DR 13.2. A7s? Print DR 14 but Screen DR 13. NOT ONE SINGLE SENSOR with 14-bit ADC output has EVER actually MEASURED more than 14 stops of dynamic range. That's because it's impossible for a 14-bit ADC to put put enough information to allow for more than 14 stops of dynamic range. There simply isn't enough room in the bit space to contain enough information to allow for more than 14 stops..not even 0.1 more stops. Every stop is a doubling. Just as every bit is a doubling. Bits and stops, in this context, are interchangeable terms. In the first bit you have two values. With the second bit, your "dynamic range" of number space doubles...you now have FOUR values. Third bit, eight values. Fourth bit, sixteen values. Fifth bit, thirty two values. To begin using numeric space beyond what the 14th bit allows, which would be necessary to start using up some of the 15th stop of dynamic range, you need at least 15 bits of information. It's theoretically, technologically, and logically impossible for any camera that uses a 14-bit ADC to have more than 14 stops of dynamic range.
Here is another fact about dynamic range. Dynamic range, as most photographers think about it these days, is the number of stops of editing latitude you have. While it also has connotations to the amount of noise in an image, the biggest thing that photographers think about when it comes to dynamic range is: How many stops can I lift this image? We get editing latitude by editing RAW images. RAW. Not downsampled TIFFs or JPEGs or any other format. RAW images. How do we edit RAW images? Well...as RAW
images. There IS NO DOWNSAMPLING when we edit a RAW image. Even if there was...who says that we are all going to downsample our images to an 8x12" print size (3600x2400 pixels, or 8.6mp)? We edit RAW images at full size. It's the only possible way to edit a RAW image...otherwise, it simply wouldn't be RAW, it would be the output of downsampling a RAW to a smaller file size...which probably means TIFF. Have you ever tried to push the exposure of a TIFF image around the same way you push a RAW file around? You don't even get remotely close to the kind of shadow lifting or highlight recovery capabilities editing a TIFF as you do a RAW. Not even remotely close. And the editing latitude of JPEG? HAH! Don't even make me say it.
Therefor, the ONLY valid measure of dynamic range is the DIRECT measure, the measure from a RAW file itself, at original size, in the exact same form that photographers are going to be editing themselves. Screen DR is the sole valid measure of dynamic range from DXO. Print DR is 100% bogus, misleading, fake.
It doesn't matter what Sony does in their BONZ X chip. The sensor output is 14-bit RAW. The only thing their BIONZ chip can do is...the same thing YOU do. They can lift shadows, and compress highlights. They can shift exposure around and reduce noise by applying detail-softening noise reduction algorithms. But then, well then you don't actually have a RAW file anymore. You have a camera-modified file. With Sony's propensity for using a lossy compression algorithm in their RAWs, you don't even get full 14-bit precision data per pixel, and that fact has shown in many cases when people go to edit their Sony RAWs in post. The compression artifacts can be extreme. I find it simply pathetic that Sony, with all this horsepower under their thumb, would completely undermine it all by storing their RAW images in a lossy compressed format. It completely invalidates the power of their sensors, and speaks to the fact that Sony is probably just as schizophrenic internally as Nikon is. That will lead to inconsistent products and product lines, poor product cohesion, lackluster design for OTHER aspects of their cameras beyond the sensor, etc. Were already seeing many of these problems with Sony cameras. Their sensors may be good, but how Sony themselves are using their sensors is crap.